EP3297831B1 - Improved method for producing a sandwich metal part having a non-developable shape - Google Patents

Description

TECHNICAL AREA

The present invention relates to the manufacture of sandwich-type parts of complex, non-developable form.

The invention applies to all technical fields that require complex shaped parts, particularly in the fields of road, air, rail and maritime transport.

STATE OF THE PRIOR ART

A sandwich-type piece generally has a honeycomb core and two skins arranged on either side of this core, and glued to it. This type of configuration allows to obtain a high rigidity while having a low overall mass. In this respect, it is noted that in known manner, the fact of removing the skins on either side of the neutral fiber makes it possible to obtain a very important moment of inertia, since this moment of inertia is proportional to the cube of the distance to the neutral fiber.

From the prior art, there are so-called "metallic" solutions consisting of making both the core and the skins of metal material, for example aluminum or in one of its alloys. These solutions usually reside in obtaining panels of substantially flat shape, including the skins bonded on both sides of the core. Optionally, the panels thus obtained are then shaped, for example by folding, bending, etc. Such a process is for example illustrated on the following web page: "Aluminum Honeycomb Panels", Aluminum Metaltek, 12.01.2015 [extract 07.03.2016], <http: // web.archive.org/web/20150112142759/http: //www.universalmetaltek.com/honeycomb_panel.htm>. However, these additional steps of recovery do not not allow to obtain final pieces of complex shapes, but at most pieces of simple shape, developable.

To produce metal parts of complex non-developable shapes, it is possible to provide a so-called "monolithic" solution in which the piece is made in one piece. Appropriate techniques such as stamping then make it possible to obtain complex shapes for the part, but the need for mechanical strength usually leads to providing a part with a large thickness, to the detriment of its overall mass. This technique may therefore be incompatible with the operating constraints encountered in certain applications, particularly in the field of transport.

Obtaining sandwich pieces of complex shapes is also possible using skins made of composite material, for example a mixture of carbon fibers and / or glass fibers with a resin. However, this technique has many disadvantages compared to the aforementioned metal sandwich solution. Among these drawbacks, mention is made of the low rigidity and the low impact resistance, the high cost of manufacture resulting in particular from the labor required to set up the folds on the tooling, the difficulty of implantation of interface elements on the composite sandwich part, the non-recyclable nature of the composite elements, the low resistance to fire-smoke criteria, etc.

STATEMENT OF THE INVENTION

The object of the invention is to remedy at least partially the disadvantages mentioned above, relating to the embodiments of the prior art.

• une étape de déformation plastique de tôles pour l'obtention des deux peaux métalliques ; puis,
• une étape de solidarisation des deux peaux à l'âme.

To do this, the subject of the invention is a method for manufacturing a sandwich-type metal part having a non-developable shape, said part comprising a metal honeycomb core and two metallic skins arranged on the one hand and another of the soul, said method comprising:

• a step of plastic deformation of sheets for obtaining the two metal skins; then,
• a step of joining the two skins to the soul.

The invention thus breaks radically with current technologies, by providing plastically deforming sheets to obtain metal skins of complex shape, even before they are bonded to the core. This technique, which is specific to the invention, offers, for the part, possibilities of final shapes which are much larger than those resulting from operations of recovery of a flat metal sandwich panel. In addition, because of the "sandwich" aspect of the part, it has a stiffness-to-weight ratio which is much more satisfactory than that achieved with the monolithic solution of the prior art. In the particular case of the transport field, it results in an energy saving for the propulsion of the transport vehicle incorporating this part.

In addition, compared with embodiments incorporating skins made of composite material, the invention confers numerous advantages, among which a higher rigidity and a higher impact resistance, a reduction in the manufacturing cost mainly due to the absence of manpower related to draping folds, greater ease of implantation of interface members on the metal sandwich piece, a recyclable character of the metal elements, or a satisfactory performance with fire-smoke criteria which improves safety passive. Also, when the piece has to be painted, the repetitions in painting are much smaller than those observed with the composite solution, which may have paint defects due to porosities on the composite part.

The invention preferably comprises at least one of the following optional features, taken singly or in combination.

The method also comprises a step of plastic deformation of the honeycomb core metal, implemented before said step of joining the two skins to this core. Nevertheless, depending on the desired final shape for the sandwich piece, this plastic deformation step is not necessarily necessary. Indeed, the only elastic deformation of the honeycomb core may be sufficient for the soul to adopt a profile identical or similar to that of the desired end piece. In the case where the elastic deformation of the core is not sufficient to achieve the desired profile, other techniques than plastic deformation can be envisaged. he This is for example one or more cuts within the soul in order to release constraints, or else the realization of appropriate machining on this soul. In both cases, this results in an increase in the elastic deformation capacity of the honeycomb core.

Preferably, when a plastic deformation of the core is implemented, elastic stretching is applied to this core during its plastic deformation. This stretching allows some sort of flattening the cells of the honeycomb, to make them adopt a shape that is closer to a rectangle than a hexagon, corresponding to the initial shape of these cells. Moreover, it is also possible to envisage a honeycomb core with cells of rectangular shape in the neutral, unconstrained state.

Thanks to the substantially rectangular stretched shape of the cells, the core has a greater capacity to deform in several directions, which facilitates the obtaining of a complex shape profile, non-developable.

Preferably, the step of plastic deformation of the sheets for obtaining the two metal skins is carried out using at least one of the following techniques: boilermaking, bodywork, incremental forming, stamping, rubber forming, thermoforming . In this regard, it is noted that the incremental forming technique is preferred for the manufacture of a small series of parts, while the stamping technique is preferred for the manufacture of an average and a large series of parts. .

Preferably, the two skins each have a thickness of between 0.5 and 3 mm, and / or the core has a thickness of between 3 and 50 mm.

Preferably, the step of joining the two skins to the core is carried out using a polymerizable adhesive, placing the skins and the core in a mold equipped with a vacuum cover. The two skins are then preferentially glued before being placed in the mold.

Finally, the skins and the core are each made of aluminum or one of its alloys, even if other metallic materials can be envisaged, without departing from the scope of the invention.

The invention also relates to a transport vehicle comprising at least one metal part obtained by the implementation of the method described above.

Preferably, it is a rail transport vehicle, but other applications are conceivable, such as a road transport vehicle, air or sea.

Other advantages and features of the invention will become apparent in the detailed non-limiting description below.

BRIEF DESCRIPTION OF THE DRAWINGS

• la figure 1 représente une vue en perspective d'un siège passager pour véhicule ferroviaire, destiné à être obtenu par un procédé selon l'invention ;
• la figure 2 représente une vue en coupe prise le long de la ligne II-II de la figure 1;
• la figure 3 représente une vue en coupe prise le long de la ligne III-III de la figure 2 ;
• la figure 4 illustre une étape de déformation plastique d'une tôle, lors de la mise en oeuvre d'un procédé de fabrication selon un mode de réalisation préféré de l'invention ;
• les figures 5a à 5f représentent différentes vues schématisant une étape de déformation plastique de l'âme en nid-d'abeilles ; et
• les figures 6a à 6d représentent différentes vues schématisant une étape de solidarisation des deux peaux à l'âme en nid-d'abeilles.

This description will be made with reference to the appended drawings among which;

• the figure 1 represents a perspective view of a passenger seat for a railway vehicle, intended to be obtained by a method according to the invention;
• the figure 2 represents a sectional view taken along line II-II of the figure 1 ;
• the figure 3 represents a sectional view taken along line III-III of the figure 2 ;
• the figure 4 illustrates a step of plastic deformation of a sheet, during the implementation of a manufacturing method according to a preferred embodiment of the invention;
• the Figures 5a to 5f represent different views schematically a step of plastic deformation of the honeycomb core; and
• the Figures 6a to 6d represent different views schematically a step of joining the two skins to the honeycomb core.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

With reference first to the figure 1 , there is shown a metal part of the sandwich type, obtained by a manufacturing method according to the invention. In this example, it is a passenger seat for railway vehicle, but the invention is not limited to this area. The invention applies in fact to the manufacture of any sandwich piece of complex non-developable shape, called complex 3D form. It can for example be a left form, double curvature, etc., as opposed to simpler forms such as flat shapes and developable. It is noted that in the context of this invention, the notion of form / developable surface corresponds to the usual definition, namely a shape / regulated surface such that the tangent plane is the same along a generator. It is therefore possible to "roll without sliding" such a shape / developable surface on a plane, the contact being along a straight line, as for a cylinder or a cone.

• siège passager (coque et structure au sein d'une seule pièce sandwich) ;
• masque de baie (pièce d'habillage pour le contour d'une fenêtre) ;
• pièce de bout : « nez » de train, de tram ou de bus ;
• capotage pour climatiseur situé au-dessus d'un bus ;
• tout ou partie d'une jante de roue de véhicule automobile.

The invention is particularly applicable to the fields of road, air, rail and maritime transport, for the production of ultra-light and ultra-rigid parts, structure or dressing of a transport vehicle. Examples of applications are given below:

• passenger seat (hull and structure within a single sandwich piece);
• bay mask (trim piece for the outline of a window);
• end piece: "nose" of train, tram or bus;
• air conditioner cowling located above a bus;
• all or part of a wheel rim of a motor vehicle.

With reference to Figures 1 to 3 it is therefore shown a metal part 1 in the form of a passenger seat for railway vehicle. This piece 1 is obtained by a manufacturing method which is specific to the present invention, and which will be described in detail below. The part 1 has a thickness that is substantially constant, for example of the order of 5 to 20 mm. Nevertheless, this thickness could vary within the part 1, without departing from the scope of the invention. The room 1 has a large dimension that can for example go from 1m to 2m, the large dimension corresponding to the maximum spacing distance between any two points of the part 1.

The piece 1 has a portion of the seat and a folder 1b. Other elements not shown are intended to be subsequently assembled on this part 1, such as for example inserts for fixing armrests, screws, reinforcing brackets, etc.

The metal part 1 is of the sandwich type, that is to say it has a honeycomb core 2 and two metal skins 4 arranged on either side of the core, and glued to it. These three components 2, 4 are made of aluminum or in one of its alloys. Each skin 4 has a thickness between 0.5 and 3 mm, while the core 2 has a thickness for example between 3 and 50 mm. Each of these three elements 2, 4 extends over the entire surface of the final part 1, adopting a global shape identical or similar to that of the same final part, while having a lower thickness. Thus, it is the superposition of these three elements 2, 4 which makes it possible to obtain the metal sandwich piece 1.

The figure 4 and the following figures illustrate a preferred embodiment of the method of manufacturing part 1. However, for the sake of clarity and understanding of the figures, part 1 has been represented in a simpler form than that of the seat shown on FIG. the figure 1 . However, as indicated above, it should be understood that the part intended to be obtained by the method according to the invention actually has a non-developable complex 3D surface, such as a left-hand, double-curved shape, etc.

The first stage of the process is schematized on the figure 4 . It consists, for each of the two skins 4, from a flat metal sheet 4 'and deform plastically so as to make it adopt a shape substantially identical to that of the final part, but with necessarily less thickness. To perform this plastic deformation, several techniques can be envisaged. One of the preferred techniques is the incremental forming adopted for the realization of a small series of pieces. This rapid prototyping technique is based in a known manner on a principle of local plastic deformation of a sheet, in order to gradually shape it. A more conventional stamping solution is preferably used for the manufacture of parts on average or in large series.

Then, it is implemented a step of plastic deformation of the honeycomb core metal, schematically on the Figures 5a to 5f .

It consists of starting from a flat honeycomb element and plastically deforming it so as to make it adopt a shape substantially identical to that of the final part, here again with a necessarily lower thickness. To perform this deformation, a honeycomb flat element 2 'is stretched in the plane of this element, as has been schematized on the Figures 5a to 5d . In other words, the stretching of the element 2 'is continued after obtaining the hexagonal shaped cells shown in FIG. figure 5c , until these cells adopt a substantially rectangular shape, shown on the figure 5d . With this stretched shape, the element 2 'has a greater ability to deform in several directions without breaking, which facilitates the obtaining of a complex shape profile, non-developable. This step is then continued by plastically deforming the stretched element 2 ', as has been schematized on the figure 5e , for example by stamping with the aid of appropriate tools 11. The stamping causes the folding of certain walls of the honeycomb element 2 ', which makes it possible to obtain the core 2 shown on FIG. the figure 5f and having an overall shape identical or similar to that of the desired final piece. The folding is more or less pronounced depending on the desired curvature.

Once the three elements 2, 4 obtained for the constitution of the sandwich part 1, it is implemented a last step of securing to fix the deformed skins 4 on the deformed core 2. This step is schematized on the Figures 6a to 6d .

To do this, the two skins 4 are first glued with a polymerizable adhesive, for example an epoxy glue. As shown in figure 6a the two skins 4 and the honeycomb core 2 are then superimposedly placed in a mold 6, the mold cavity 8 of which has a shape corresponding to that of the outer surface of the skin 4 located below in the stack. As illustrated by figure 6b , the step is continued by placing a vacuum cover 10 on the upper part of the mold, so that it matches the outer surface of the skin 4 located above in the stack.

Then, the Figure 6c shows that a depression is applied in the space between the body of the mold and its cover 10, so that the latter exerts a uniform pressure on the stack of elements 2, 4. The applied depression is to about 0.9 bar, which allows to obtain a pressure of the order of 9t / m ² .

Once the polymerized glue, the finalized part 1 can be extracted from the mold, as is schematized on the figure 6d .

Of course, various modifications may be made by those skilled in the art to the invention which has just been described, solely by way of non-limiting examples.

Claims (10)

1. A method for producing a sandwich type metal part (1) having a non-developable shape, said part comprising a metal honeycomb core (2) as well as two metal skins (4) arranged on either side of the core, said method comprising:

   - a step of plastically deforming metal sheets (4') for obtaining both metal skins (4); and then

   - a step of securing both skins (4) to the core (2).
2. The method according to claim 1, characterised in that it also comprises a step of plastically deforming the metal honeycomb core (2), implemented before said step of securing both skins to this core.
3. The method according to claim 2, characterised in that during said step of plastically deforming the metal honeycomb core (2), an elastic stretching is applied to said core.
4. The method according to any of the preceding claims, characterised in that the step of plastically deforming the metal sheets (4') for obtaining both metal skins (4) is made using at least one of the following techniques: sheet-metal work, body making, incremental forming, drawing, rubber forming, thermoforming.
5. The method according to any of the preceding claims, characterised in that both skins (4) each have a thickness between 0.5 and 3 mm, and/or in that the core (2) has a thickness between 3 and 50 mm.
6. The method according to any of the preceding claims, characterised in that the step of securing both skins (4) to the core (2) is made using a polymerisable adhesive, by placing the skins and the core in a mould (6) equipped with a vacuum bag (10).
7. The method according to claim 6, characterised in that both skins (4) are adhered before being placed in the mould (6).
8. The method according to any of the preceding claims, characterised in that the skins (4) and the core (2) are each made of aluminium or one of its alloys.
9. A transport vehicle, characterised in that it comprises at least one metal part (1) obtained by implementing the method according to any of the preceding claims.
10. The vehicle according to claim 9, characterised in that it is a railway transport vehicle.

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